Libya faces civil war and "rivers of blood", the son of its leader Moamer Kadhafi warned on Monday, as a brutal crackdown failed to stop an unprecedented popular uprising from reaching the capital.

With gunfire crackling in the streets of Tripoli, and Human Rights Watch putting the death toll at 233 since Thursday, Saif al-Islam Kadhafi vaguely promised reforms as he condemned the revolt as a foreign plot.

"Libya is at a crossroads. If we do not agree today on reforms... rivers of blood will run through Libya," he said in a fiery but rambling televised speech that betrayed a note of desperation within his father's 41-year regime.

"We will take up arms... we will fight to the last bullet. We will destroy seditious elements. If everybody is armed, it is civil war, we will kill each other... Libya is not Egypt, it is not Tunisia."

The elder and famously mercurial Kadhafi, 68, the longest-serving leader in the Arab world, remained out of sight.

Heavy gunfire broke out in central Tripoli and several city areas on Monday for the first time since the uprising began in eastern Libya, witnesses and an AFP journalist reported.

"We can hear gunfire outside. It hasn't stopped all day," the resident of a suburb east of Tripoli told AFP in Cairo by telephone.

"When we heard the unrest was approaching, we stocked up on flour and tomatoes. It's definitely the end of the regime. This has never happened in Libya before. We are praying that it ends quickly."

"Our neighbor was killed last night," added another Tripoli resident in the centre of the capital. "There is a lot of shooting outside. No one from our family has gone to work today."

Several witnesses said fire had been set to public buildings overnight, including the state broadcasting offices and branches of the People's Committees that are the mainstay of the regime.

Some 500 Libyans meanwhile stormed and looted a South Korean construction site near the capital on Monday, injuring about 15 Bangladeshi as well as three South Korean workers, Seoul's foreign ministry said.

Earlier, witnesses reported clashes in Tripoli's downtown Green Square between protesters and Kadhafi supporters, and a resident of the working-class Gurgi area said security forces had fired tear gas at protesters.

"We are hearing anti-regime slogans and firing," he told AFP by telephone overnight Sunday. "Our house is filled with tear gas."

In London, British energy giant BP said it was preparing to evacuate some of its staff from Libya, which holds Africa's biggest oil reserves.

In Brussels, Spain's Foreign Minister Trinidad Jimenez said the 27-nation European Union was "coordinating the possible evacuation of EU citizens coming from Libya, especially from Benghazi."

In Cairo, Libya's envoy to the Arab League said he had resigned to "join the revolution."

Tripoli's ambassador to Delhi also quit, as did a lower-level diplomat in Beijing who said Kadhafi may have left the country, Al-Jazeera television reported.

The United States and the European Union strongly condemned the use of lethal force, while UN Secretary General Ban Ki-moon called for "the non-use of force and respect for basic freedoms".

Saif al-Islam Kadhafi, 38, who holds no formal government post but wields vast influence as his father's heir apparent, suggested that Benghazi, long an opposition hotbed, was out of government control.

"At this moment there are tanks being driven by civilians in Benghazi," he said, insisting the uprising was aimed at installing Islamist rule and that it would be ruthlessly crushed.

Separately, Prime Minister Baghdadi Mahmudi told EU ambassadors in Tripoli on Sunday there were "very precise plans, destructive and terrorist, that want Libya to become a base for terrorism."

Underscoring Libya's vast oil wealth, the younger Kadhafi said: "We have one resource that we live on and that is petrol. All the foreign companies will be forced to leave the country.

"This is an opposition movement, a separatist movement which threatens the unity of Libya," Kadhafi said in the speech which blamed Arab and African elements for fomenting the troubles.